No more premium gas cars for me

Acura CSX Type S which also says 'Premium Unleaded Fuel Only' on the filler door and 'Premium Unleaded Required' in the owner's manual. 9 years old and 140,000 miles almost all of which has been with regular unleaded. No noticeable difference in mileage between the two fuel types and no engine issues. I'm not a racer but highway speed is not infrequently 85 mph and I have 'fun' driving it.
 
looked at the pump last night, high test is only 25 cents more than 87 octane
 
Big_Hitter said:
looked at the pump last night, high test is only 25 cents more than 87 octane
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I picked the wrong state to own a car that requires premium. Premium costs $.55-$.60 more per gallon that regular. According to GasBuddy most states have closer to half that difference.
 
MichaelB said:
Our car was purchased new in '06. Back then the difference between regular and premium gasoline was $.20 per gallon. I did the numbers, expected the additional fuel cost would be around $75 per year, so we went for it - a car that requires premium fuel.

The additional cost for premium gas then rose to $.25. 2 years ago it rose to $.50. late spring this year is went to $0.60, and yesterday at Costco it was at $0.70. We put 15k miles per year, get around 23mpg, so the additional cost is now over $400. It won't break the bank, but over 5 or 6 years it is a sizable amount of money.

Premium gasoline - first and last time for us.
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We've got an '06 ES330, and there is no reason that vehicle should have a motor which runs high compression. DW complains about the premium, but we've averaged 7k-8k miles per year since we bought the car in late '08. Lexus has actually stopped putting high compression motors in their vehicles I believe, at least in the "granny" cars.

One other consideration is one's atmospheric pressure. Here in Denver, the highest octane we can get is 91. My other vehicles take 85. But, the higher the altitude, the lower the Patm and the less like likely hood of pre-detonation. There is play within the ECU to adjust for small changes in timing, but if it senses a knock it will go into "safe mode" and it limp around.

With that said, how little we drive the vehicle and we are looking to sell in the next 6 months (DW wants a bigger vehicle and we're expecting a 3rd child), we are just going to run premium until we can sell it. And yes, the new vehicle will take the gasoline commoners use. :cool:
 
The only somewhat modern vehicle I've ever owned that requires premium is a 2000 Park Avenue Ultra, which is supercharged. I'll admit I've put 87 octane in it on occasion, and never noticed a difference. But, I never did that back-to-back, so there was always some 93 octane in the tank for it to mix.

My understanding with modern cars is that they're "smart" enough to adjust the spark timing and other functions when you put a lower octane fuel in, and in most day to day driving, you won't notice much of a difference. But, if you tend to drive hard (high speed, fast acceleration, etc) you might notice. And, fuel economy might suffer a bit as well, but again, if you're an aggressive driver you're going to be guzzling a bit, anyway.

I've heard that Chevy/GMC pickups with the old 4.3 V-6 could actually get messed up if you put premium in them! They were designed to run on 87 octane, and normally, when you put premium in a vehicle that only needs regular, you're just wasting money but doing no harm. However, with the 4.3, it would actually mess up the engine if you did it too much.
 

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Andre1969 said:
My understanding with modern cars is that they're "smart" enough to adjust the spark timing and other functions when you put a lower octane fuel in, and in most day to day driving, you won't notice much of a difference.
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The concern of pre detonation is on the compression stroke, not the ignition/combustion stroke. A vehicle's ability to adjust for this via timing is case by case and depending on when the detonation is happening on the compression stroke. The ECU may be able to compensate by adjusting air/fuel ratios, but it only goes so far.

What one notices and doesn't notice, may or may not be helpful. YMMV. Surely, the safe thing to do is to run the mfg recommendation. One could most likely have their vehicle tuned or sell it. But trading cars is almost always a losing endeavor for finances.
 
My Audi Q5 "requires" Premium. The manual says the car will operate with Regular, but to replace with Premium as soon as practical, or something to that effect. In my area, Premium is 93 Octane, and my car requires 91 Octane. So, when I remember I will alternate fill-ups, when car is half-full, with mid-grade. However, I don't keep religious track of this; life is too short and I bought the car knowing it requires Premium.
On a sort of related note, before buying the Q5 I considered the Volvo. It called for Regular, but got less MPG. I did a gross calculation of the relative costs, and the Q5 with Premium came out much cheaper -- i.e., the gas usage costs.
 
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Andre1969 said:
The only somewhat modern vehicle I've ever owned that requires premium is a 2000 Park Avenue Ultra, which is supercharged. I'll admit I've put 87 octane in it on occasion, and never noticed a difference. But, I never did that back-to-back, so there was always some 93 octane in the tank for it to mix.

My understanding with modern cars is that they're "smart" enough to adjust the spark timing and other functions when you put a lower octane fuel in, and in most day to day driving, you won't notice much of a difference. But, if you tend to drive hard (high speed, fast acceleration, etc) you might notice. And, fuel economy might suffer a bit as well, but again, if you're an aggressive driver you're going to be guzzling a bit, anyway.

I've heard that Chevy/GMC pickups with the old 4.3 V-6 could actually get messed up if you put premium in them! They were designed to run on 87 octane, and normally, when you put premium in a vehicle that only needs regular, you're just wasting money but doing no harm. However, with the 4.3, it would actually mess up the engine if you did it too much.
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Can you give some real backup for that stmt on the 4.3 engine? With my limited knowledge I cannot see how having higher octane could mess up an engine at all... there is nothing that the higher octane can do to mess it up.
 
Slow But Steady said:
So the lower trace is the 91 octane torque and HP, and the higher one is the E85?

Were there other mods to the car besides the injectors and the fuel pump?

Thanks!
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Yes

Cobb AP protune, Cobb CAI, Crawford AOS, VF52 turbo, Perrin catback, CNT downpipe, SRTI gauges, bulletproof TMIC mod, 2" lift

I think that's about it


I used to take my car to enginelogics in Stafford for performance work/tuning when I lived in Houston.
 
Both of our vehicles have high compression engines that require 91 octane or better. The engine computers will compensate for lower octane fuel but there will be a performance and mileage penalty.

The price differential between the two grades of fuel is not something that I'm currently concerned with, nor would that drive the selection of a new vehicle.

Driving around town or locally the savings would be negligible. Any longer distance trips that we take usually involves a rental car for reliability concerns, and the fuel selection is out of our hands.

If cost per mile is a major concern, why not consider a diesel, such as the TDI? I hear they get fantastic mileage, and low emissions too.:cool:

_B
 
Texas Proud said:
Can you give some real backup for that stmt on the 4.3 engine? With my limited knowledge I cannot see how having higher octane could mess up an engine at all... there is nothing that the higher octane can do to mess it up.
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I tried Googling but can't find anything. And you'd think that if it was a common problem, it would come up pretty easily. The way I found out about it was that I had a friend who had an '05 Silverado with the 4.3, and we had gotten into a discussion about octanes. He said that too high of an octane could hurt an engine. I said that was BS...that if an engine wasn't designed for it you're just wasting money, but it wasn't harmful.

This guy was one of those "I always have to be right" types and we got into an argument about it. Like you, I just couldn't understand how a higher octane could hurt an engine. But, he was adamant about it. At the time, I was able to find some corroboration that actually backed him up online, but that was about 6 years ago, and I can't remember what it was, or how "official" it was.

So, what I heard could just be an old wives' tale. Another one of those anecdotes I heard was the 2.7 V6 my old 2000 Intrepid had was similar enough with the programming, intake, fuel injection, or whatever to the 3.5 used in the Intrepid R/T and Chrysler 300M, that if you put 93 octane in it, you'd get better performance up to about 90% of wide-open-throttle.

I don't know if it was true or not, though. One thing I did discover though, is that if you floored it, as soon as the car hit the rpm where the horsepower peaked, around 6000 rpm, it would upshift immediately, even though redline was around 6500 I think. However, the torque peaked at around 4900 rpm, and I discovered that if you floored it, but then let off a bit once it hit 4900 rpm, it seemed like it helped with acceleration. I don't know if it really did, or if it was just in my mind.
 
I'm no expert, but a pretty decent back yard mechanic and here's my take. Regardless of Octane in the tank, you can get almost any engine to knock by feeding it the wrong mixture for a given engine RPM. For instance, drive your vehicle up a descent size hill without pressing on the gas pedal to increase the RPM and it will eventually bog down (RPM will decay). Then press the gas pedal slightly and it will more than likely start to knock on you. And yes, knocking, or pre-ignition, is not good for your engine. However, an occasional knock is not going to lead to engine replacement for most.

Now, 50 years ago, before modern ignition systems, engine problems cause by excessive knocking was more common. In today's engine not so much. That issue really went away with the 15K mile tune-up from the 60s. Hell, I still have the original spark plugs in my 100K mile Camry engine. Runs like a top.

The only time I consider premium gas if I'm driving in the mountains where there will be a considerable amount of hill climbing. That when I risk the excessive knocking.
 
NanoSour said:
I'm no expert, but a pretty decent back yard mechanic and here's my take. Regardless of Octane in the tank, you can get almost any engine to knock by feeding it the wrong mixture for a given engine RPM.
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I'm not an expert either, but experts have told me that modern engine control systems will cut timing when they detect knock, and if they still detect knock, they will dump in fuel. So you could probably get it to knock, but it wouldn't knock for long.

I still wouldn't try this with a purpose-built high horsepower engine.
 
Here's an explanation for part of the increase in higher octane gasoline. As pump prices drop, U.S. motorists splurge on premium gas | Reuters
For the second time in the past decade, a sharp fall in pump prices has triggered a spike in demand for the higher-octane fuel that has far outpaced the overall rise in consumption.
In the first four months of the year, sales of premium grade gasoline - which makes up around a tenth of the market - surged by 12.6 percent, according to the latest data available from the U.S. Energy Information Administration. Regular grade sales rose by only around 3.7 percent during the period.
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As the price for gas falls, some motorists switch from low to higher octane.
 
Just sold my premium gas car (Subaru Legacy GT) today... sorta sad... I really liked the car but we needed something bigger and it was so low DW was uncomfortable getting in and out of it. I'll miss the performance though.
 
pb4uski said:
Just sold my premium gas car (Subaru Legacy GT) today... sorta sad... I really liked the car but we needed something bigger and it was so low DW was uncomfortable getting in and out of it. I'll miss the performance though.
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oh man I love LGTs - those are fun (and they don't make them anymore)
 
MikeD said:
I think that may be a non-sequitur.

Mike D.
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Well, I was quoting about mileage, so the second one was referring to that....


But, I can see how a quote out of context does look strange....
 
My gas hog suburban 7.4 engine runs fine on regular.

My 95 Jaguar prefers mid grade gas. Per the design engineer of the ignition and fuel control computer and frequents one of the jaguar forums the design was for what we in US call mid grade gasoline.

The top tier is pure waste of money, while the low grade will cost performance when you stick your foot in it (big time) also in normal driving (not so much). The ignition control program has the ability to retard ignition timing on a per cylinder bases, the knock sensor is a superb design. He also noted that original design was a bit conservative and an additional 5 degrees of timing advance overall is permissible. Can do up to 7 degrees but the knock sensors would be more active negating the occasional benefits.

Unlike some GM designs, the crankshaft pickup location which determines base timing can be modified on the Jaguar 6 cyl inline engine. I have done so. It is noticeable and verifiable improvement via butt dyno, real dyno and MPG.
 
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